AT least two passengers on the missing Malaysia Airlines flight travelling on false passports have become the focus of a grim investigation as aviation and security experts claimed a bomb was the most likely cause of a crash believed to have claimed 239 lives.

As two RAAF P-3C Orion aircraft set off from Darwin to join the search for Malaysian Airlines flight MH370 in its third day, fears are mounting that the flight’s 239 passengers — including six Australians and two New Zealanders — have been murdered.

A relative of a passenger onboard Malaysia Airlines flight MH370 cries out at a local hotSource:Getty Images

A stolen Austrian passport gave one passenger access to the plane.Source:Supplied

Malaysian authorities have activated counterterrorism units to “look at all possibilities” as the FBI prepared to send agents to Kuala Lumpur last night to investigate the flight, which disappeared without any warning or contact south of Vietnam about 1.30am local time on Saturday morning.

And there are concerns the tragedy could be linked to anti-Chinese separatists responsible for a savage knife attack that left 33 dead at a Yunnan railway station on March 1.

It comes as aviation and security experts said a bomb was the most likely cause of the crash, because a catastrophic blast would be needed to take down a Boeing 777.

FBI agents will help review video from the Kuala Lumpur airport for images of departing passengers that can be checked in the FBI’s vast counterterrorism database.

Australian National University’s Michael McKinley said it would take some sort of explosion for the aircraft to fall from the sky so suddenly.

The Malaysia Airlines Boeing 777-200ER that disappeared from air traffic control screensSource:AP

“I think an explosion is more likely than a hijacking. Most of these sophisticated transport aircraft have a hijack warning system so they’re able to broadcast that. But when you get no distress signal, you’re dealing with a catastrophic event. That suggests some form of explosion,” Dr McKinley said.

Terror in the skies

June 1, 2009:

228 passengers and crew died when Air France Flight 447 from Rio de Janeiro crashed into the Atlantic Ocean. Malfunctioning airspeed indicators were found to be the cause of the accident.

November 21, 2001:

265 people died when American Airlines Flight 587 crashed shortly after taking off from John F. Kennedy International Airport in New York.

The first officer’s overuse of the rudder in response to turbulence created by another plane was blamed. for the crash

September 11, 2001:

2977 people died when four aircraft travelling from the Californian US east coast airports to California were hijacked by terrorists. American Airlines Flight 11 and United Airlines Flight 175 both flew into the twin towers of New York’s World Trade Centre, destroying both buildings. American Airlines Flight 77 crashed into the Pentagon and United Airlines Flight 93 crashed into a Pennsylvania field.

July 25, 2000:

113 people died when Air France Flight 4590 — a Concorde — crashed shortly after takeoff from Paris when an aircraft part lying on the runway ruptured its fuel tank.

July 17, 1996:

230 people were killed when TWA Flight 800 exploded and crashed into the Atlantic Ocean 12 minutes after taking off from John F. Kennedy International Airport in New York. An explosion in a fuel tank was found to be the most likely cause.

December 21, 1988:

270 people died when Pan Am Flight 103 was destroyed by a bomb over the town of Lockerbie, Scotland. The bomb was later found to have been placed on-board the Boeing 747 by Libyan agents.

August 12, 1985:

520 people died when a bulkhead tore open on board Japan Airlines Flight 123, ripping off its tail. The pilots fought for half an hour to keep the plane airborne before crashing into a mountain.

June 23, 1985:

329 people killed when a bomb exploded in the hold of Air India Flight 182 off the southwest coast of Ireland. Sikh extremists were later found to be responsible for bombing of the Boeing 747.

A new theory also emerged that radar may indicate that the missing aircraft may have attempted to turn back.

Malaysia’s air force chief Rodzali Daud revealed the possibility but he declined to give any details of how far it may have veered off course.

Meanwhile a passport puzzle has arisen with the revelation that at least four passengers may have boarded the Beijing-bound flight with false documents.

A woman cries at the arrival hall of the International Airport in Beijing, ChinaSource:AP

Citizens from 14 nations were on board the missing flight although most were Chinese nationals. Chinese media reported yesterday that two of the passengers on fake passports were travelling together and had bought their tickets through China Southern, on a code-share with Malaysian Airlines.

An Austrian named Christian Kozel had his passport stolen in Thailand in 2012, while the passport of Italian Luigi Maraldi was stolen in Thailand last year. Despite their names being on the passenger manifest, neither man was on the flight.

Devoted Brisbane pair Catherine and Robert Lawton are among the missing.Source:Supplied

Transport Minister Hishammuddin Hussein yesterday said Malaysia was investigating four names on MH370’s flight manifest. When asked to confirm local media reports that another two suspect passengers had been identified, he said: “All the four names are with me.”

The Chinese official Xiamen Daily reported that one of the passengers who was supposed to be on the flight, according to the manifest, was at home in China.

Associate Professor Felix Patrikeeff, of Adelaide University, said he was concerned by the number of Chinese passengers on board and it may have been targeted by the an anti-Chinese group such as the Uighur militants from China’s restive Xinjiang province in the country’s northwest who attacked commuters in Kunming on March 1.

Prof Patrikeeff said the plane may have been targeted as a result of the number of prominent artists and calligraphers on board — skills revered by the Chinese.

“So if one wanted to strike a blow for the sake of symbolism, you could say that that’s not a bad place to start,” Prof Patrikeeff said.

Prime Minister Tony Abbott confirmed the RAAF had deployed two P-3C Orion aircraft previously involved in Operation Sovereign Borders to Malaysia to help search efforts already being conducted by more than 40 ships and 22 aircraft from five nations.

They will be replaced by two P-3Cs from RAAF Edinburgh north of Adelaide.